Imaging systems that are capable of imaging films, lithographic plates, flexographic plates, proofing materials and other media types are well known in the art. In the printing industry, laser based exposure heads are commonly used to form an image on a lithographic plate for subsequent use in a printing operation on a printing press. Some imaging systems are capable of printing on multiple media formats such as plates, films, and proofing media.
A common imaging system architecture provides an exposure head which generates one or more modulated beams or channels and an imaging media carrier for securing a media sheet. The beams are scanned over the media by a scanning means which produces relative motion between the media sheet and the beams. The scanning means may comprise, for example, an external drum, internal drum, or a flatbed scanning system. In an external drum system the media is held on a rotatable drum and the beams from the exposure head are scanned over the media surface by a combination of drum rotation and translation of the exposure head.
A common problem in the design of imaging systems is providing sufficient imaging speed to meet the media preparation requirements of the industry. Particularly in the printing industry, where a large capital investment in printing press equipment dictates that presses should be kept running at high duty cycles, the time taken to prepare a plate for press may be a limiting factor in the printer's overall workflow.
U.S. Pat. No. 5,887,525 to Okamura et al. describes a machine for simultaneously making two printing plates for newspaper printing. The machine has two exposure sections in series to speed up the production of plates for a newspaper press. In U.S. Pat. No. 5,795,689 to Okamura et al. the speed of a machine for making newspaper printing plates is increased by using two exposure heads in parallel to scan different areas of a plate, thus reducing the time taken to prepare a plate for use on the press. The exposure heads may each write images that are duplicates or the image written by each exposure head may be different.
U.S. Pat. No. 5,934,195 to Rinke et al. describes a flatbed system that is capable of simultaneously exposing two separate single-wide plates, each having the same or a different image thereon, or a single double-wide plate, each half of which has the same or a different image thereon.
There remains a need for better methods and apparatus for imaging with multiple exposure heads.